In the semiconductor fabrication process, a square cross-sectional or rectangular cross-sectional container made of a plastic material is frequently used to transport articles. These articles may include silicon wafers, reticles or other substrates used for building IC devices. A reticle is a transparent ceramic substrate that is coated with a metallic layer forming a pattern for an electronic circuit. It is generally used in an imaging step during a photolithographic process wherein a pattern of a circuit is reproduced on the surface of an electronic substrate, i.e., on a wafer surface.
A reticle can be constructed of any suitable transparent ceramic materials. One of the most commonly used material is quartz or silicon dioxide. A quartz reticle can be readily coated with a chrome layer at selective areas to reproduce an electrical circuit. The chrome metal layer may be formed by either a pure chromium or a chromium alloy. During a photolithographic imaging process, a light source is projected from one side of the reticle that is coated with the pattern such that the pattern can be reproduced on the surface of a wafer which is positioned on the opposite side of the reticle. The pattern for the electronic circuit coated on the reticle is frequently laid out in a 533 magnification. The true dimensions of the electronic circuit reproduced on the wafer surface can be obtained by suitably adjusting the optical lenses situated between the reticle and the wafer. Metallic coatings other than chrome may also be coated on the surface of the reticle for the circuit lay-out. However, chrome has been found to be an ideal material for its appearance of a brownish tone and its ease of identification by human eyes.
In a semiconductor fabrication facility, static electricity or electrostatic discharge frequently develops on surfaces of articles made of insulating materials when they are touched or rubbed by other insulating materials such as insulating gloves. The electricity is produced based on a triboelectricity theory. The discharge of the static electricity to machines and to human operators can cause damages to semiconductor wafers and process tools. Sometimes, it may even cause injury to a machine operator. In a semiconductor fabrication facility, it is therefore necessary to control ESD by grounding the machines, by controlling the relative humidity, or by building walls and floor coverings with slightly conductive materials such that electrical charges can be routed to ground. When the triboelectricity is suitably controlled, the control of dust and particulate contamination is also enhanced. For instance, the metal racks, pipe lines, cabinets, cables and rails are normally grounded in a facility to an equal potential bar or to a planar ground. The metal pedestals of the raised floor are then connected to the planar ground under the raised floor. To further enhance ESD protection, the metal framework of the clean room wall systems are also connected to the planar ground. Air ionization systems are frequently installed at selected locations in a fabrication facility, to provide additional ESD control.
Despite the elaborate efforts spent in grounding process machines and various facilities, ESD damages still occur in a fabrication facility. A typical example is the occurrence of ESD when an insulating material is shipped or transported in a container made of another insulating material. For instance, when a reticle is transported from a storage facility to a photolithography machine in a container, i.e., a pod, that is normally constructed of a thermoplastic material. Since the reticle itself is an insulating material, i.e., a quartz or other silicon dioxide materials coated with a chrome coating, when the pod is handled by machine operators wearing insulating gloves, the static charge on the pod drastically increases due to friction generated between two insulating articles. Since the pod is not equipped with an anti-electrostatic device, high static electricity cumulates on the surface of the pod. For instance, it has been confirmed that the static electrical field generated on a pod surface increases from 0.1 KV/inch to nearly 15 KV/inch when a polycarbonate pod is rubbed with PVC gloves. Such a high static electricity build-up on the surface of the pod immediately causes an electrostatic discharge between the pod and the reticle contained therein. When ESD occurs between the pod and the reticle, the pattern on the reticle surface is usually damaged to such an extent that it can no longer be used for imaging. Conventional air ionization devices installed at a fabrication facility are not useful for preventing such ESD damages.
Others have proposed techniques for controlling or minimizing ESD damages to reticles carried in plastic containers. For instance, anti-electrostatic-type plastic materials, such as Bayon.RTM. has been used for the construction of the pod. However, due to its high cost, this type of anti-electrostatic plastic material cannot be widely utilized in a fabrication facility. Still others have proposed the use of gloves that are made of a conductive material such as Propex.RTM. so that the generation of electrostatic discharge can be avoided. The high cost of the Propex.RTM. gloves prohibits its broad usage in the processing industry.
In some of the newer models of the reticle pods, the internal moving parts are provided with ESD metal mask shield to eliminate electrostatic discharge. However, there are no provisions for preventing a stepper mask pick-up arm from generating ESD during its movement in picking up a reticle. For instance, one of such stepper mask arm 60 is shown in FIG. 3. During an attempt of the stepper mask arm 60 in picking up reticle 24, the bottom surface 26 of the reticle inevitably slides on the tips of pedestals 22, as shown in FIG. 1.
Referring initially to FIG. 1 where it is shown a cross-sectional view of a container equipped with a conventional reticle support system. The container 10 is constructed of a top lid 12, a bottom lid 14, a left sidewall 18 and a right sidewall 16. The front and rear sidewalls (not shown) are constructed of similar materials, i.e., a thermoplastic material such as polycarbonate or polymethylmethacrylate. Pedestals 22 are positioned on the bottom lid 14 of the container for supporting a reticle 24. The reticle 24 is normally constructed of a transparent ceramic material such as quartz or other types of silicon dioxide. On a surface 26 of the reticle 24, a pattern 28 is formed by coating the surface with a suitable metallic material. The pattern 28 can be formed by one of many suitable metallic materials. A handle 32 is affixed to the top lid 12 of the container 10 for easy carrying by an operator. The d.sub.2 value for the commercially obtained container is 3.365 cm.
The scratching of the reticle surface 26 during its removal procedure from the pod 10 can cause a serious contamination problem. As shown in FIG. 2, a plane view of the reticle 34 with two alignment marks 20 situated in the surface 26. The position of the pedestals 22 for supporting the reticle 24 are shown in ghost lines. During the reticle removal process, the surface 26 is dragged on the tip of the pedestals 22 and therefore, not only the frictional force may cause scratching of the alignment marks 22 and thus cause misalignment, the frictional force on the surface 26 may also cause particle contamination from the reticle material. Moreover, electrostatic discharge may be generated by the friction between two electrically insulating articles, i.e., between the pedestal 22 and the quartz surface 26.
It is therefore an object of the present invention to provide an electrostatic discharge-free container for holding insulating articles that does not have the drawbacks or shortcomings of the conventional containers.
It is another object of the present invention to provide an electrostatic discharge-free container for holding insulating articles that is provided with support means for supporting the insulating articles thereon and for preventing ESD when the article is moved on the support means.
It is a further object of the present invention to provide an electrostatic discharge-free container for holding insulating articles that utilizes support means constructed by a support base and a roller.
It is another further object of the present invention to provide an electrostatic discharge-free container for holding insulating articles that utilizes support means which are fabricated of electrically conductive materials.
It is still another object of the present invention to provide an electrostatic discharge-free container for holding insulating articles that utilizes support means for the insulating article that are fabricated of electrically conductive material and are grounded by a grounding wire.
It is yet another object of the present invention to provide an electrostatic discharge-free container for holding insulating articles that is capable of preventing scratching of the article when it is moved on a support pedestal.
It is still another further object of the present invention to provide an electrostatic discharge-free container for holding insulating articles that utilizes roller support means for preventing scratching of the article surface and resulting particle contamination in the container.